Atmospheric vaporizer



Feb. 18, 1958 R. c, ENGER ETAL ATMOSPHERIC VAPORIZER 2 Shets-Sheet l Filed July 24, -1955 INVENTORS ROBERT QENGER FORD R. PARK,JR.

l Feb. 18, 1958 R. c. ENGER ETAL 2,823,521

ATMOSPHERIC VAPORIZER Filed July 24, 1955 2 Sheets-Sheet 2 INVENToR ROBERT c. ENER Fono R.PARK,JR

BYWM A RNEY FIN THICKNESS INCHES United States Patent ATMOSPHERIC VAPORIZER Robert C. Enger, Buffalo, and Ford R. Park, Jr., Snyder,

N. Y., assignors to Union Carbide Corporation, a corporation of lN ew York Application July 24, 1953, serial No. 370,157

z claims. (ci. sz-i) equipment, such vaporizers are usually located out-of- Vdoors where they are subjected to extreme atmospheric conditions which greatly complicate the problem of providing a simple and highly efficient atmospheric vaporizer. During certain .periods lof the winter, severe atmospheric conditions `are encountered wherein the air temperature and relative humidity are such as to cause heavy ice and -frost deposits to Yform on the coils and ns of nned-tube ytype atmospheric vaporizers operating under these Acondi- 4tions. These ice and frost deposits are in some cases sufciently thick to block the circulating air passages and greatly reduce the heat transfer to the volatile 'liquid thereby causing a failure in vaporization.

The worst operatingY conditions for atmospheric vaporizers are in the -40 F. ambient air region with high (100%) relative humidity, as heavy ice deposits are formed in this frange. rl`he usual severe winter weather of 0 F. or below is not as critical, as the bulk of the resultant frost deposit is blown off the heat transfer sur- 'faces by the vaporizer fan.

The power requirements of atmospheric vaporizers are considerably less than lother 'vaporizing means such as steam and electricity; consequently, such vaporizers may be practically installed in mobile volatile liquid 'transport units where it is desired to transport the payload as a liquid, but distribute it as a gas with 'a limited power supply.

"Itvis, -the`1'efore, an object of the present invention to provide a simple and highly eiiicient atmospheric vaporlizerh'rough lwhich atmospheric vair and the liquid to 'be vaporized are passed in heat exchange relation.

Another object is to provide such an atmospheric vaporizer which will successfully vaporize volatile liquids even under the most adverse winter atmospheric conditions to be encountered.

A still further object is to provide such an atmospheric vaporizer having a size and weight sufficiently small for vease'fin portability.

Other :aims and advantages of the invention -willbe apparent from -the following description and'appended claims.

`In theaccompanying drawings:

Fig-1 .is a-side view,rmainly in cross-section, of an atmospheric vaporizer embodying the present inventiomthe section being taken .along the line 1-1 of Fig. 2;

Fig. A2, is afront view, partly broken-away,.of theatmospheric vaporizer of Fig. 1;

Fig. 3 is an elevational view, partly in section, of a modified tube arrangement to be employed in an atmospheric vaporizer embodying the invention which is capable of below critical pressure operation; and

Fig. 4 shows a series of curves graphically representing the relationship betweenheat transfer rate,vn thickness, and coil spacing for two of the different materials which may be employed as-the iin and coil material in the atmospheric vaporizer of the present invention.

In accordance with the present invention, and referring to the embodiment shown in Figs. 1 and 2 of the accom-- panying drawings, an atmospheric vaporizer V is provided having an outercasing 1, a plurality of tins 2 of copper,

laluminum or other-suitablefmaterial, arranged parallel t0 "each other and tothe axis of the outer casing, a plurality of serpentine tubes 3 of copper or other suitable material each secured 'to-fin Y2', and connected in parallel, and a fan l4` positioned attone end for forcing a stream of atmospheric airthrough the space between the plurality of fins 2 and 'tubesi The tubes are secured against the'ns so as to provide suitable metallic heat conductive paths between the tubes and fins; for example, thestubesmay be metal-bonded to thefins Iby lsoldering .or brazing, depending on the materials usedfor the tubes and fins.

The inlet -and :outlet ends of the plurality of serpentine tubes Yare `connected with an inlet manifold 5 and an outlet-'manifold 6, respectively. At both the inlet and outlet `ends of serpenti-ne 'tubes 3, expansion loops or bendsr7 and 8, respectively, yare provided to allow the system -.to

.adjust to any mechanical .expansion or contraction due to :changes in temperature. AShaft support bracketfmeans i9 .is' provided to :support the `fansl'iaft Vat one zend of ,the

outer casing.y The members 10 are provided ,to .guard against the passage of objects into fthextfan, Aaswell .tasa/to helpstructurallty .strengthen the extension i outer casing 1., and Support shaft support means 9.

Thie'inlet tube arrangement illustrated fin Figs. :1 and 2 is 'suitable for vapori-zing and 'superheating a volatile liquidratany pressure, but is preferred for :operation above the critical pressure.

It `Vhas been found that ,there ,are many variables encountered in ithe design y.of an atmospheric v aporizer .of

theoretically developed lto correlate .results obtained :by

testing 'atmosphericvvaporizers of :this jtype under .widely yvaryin g #conditions Q:total rate of heat .transfer from airto volatile liquid v(Bft. .u /hrJ/sg. ftj).

vk=coefticient of thermalconductivity Vof n(B. t. 11./ hr. s q. ft./ 'l/f).

17A=inlet .atmospheric .air .temperature F.)

Tv=inlet volatile liquid temperature F.).

hA--lair side film coefficient (B. t. u./hr./sq.` ft./ F.).

hv=volatile liquid side film coefficient (B. t. u./hr./ Sq. ft./ E).

L=1/z space between adjacent tubes (ft).

a=volatile liquid side area for 1 foot of length (ft2).

B :V 2h A ic N :number of vaporizer fins.

This equation is graphically represented in Fig. 4 of the drawing which shows the relationship between rate of heat transfer and fin thickness for a series of tube spacings. The curves are for copper and aluminum tubes and fins, but the equation may be applied to fintube atmospheric vaporizers of any material. It is also pointed out that the total rate of heat transfer is equal to the numbers of fins employed in the vaporizer multiplied by the heat transfer rate per fin.

The above-stated equation does not include fin spacing as a variable factor as it is relatively easy to empirically determine this factor for specific applications. It is necessary to position the fins sufficiently far apart to maintain internal air passages through the vaporizer assembly during severe weather conditions in which the fins are partially covered with frost or ice.

For operation below the volatile liquid critical pres-v sure, it is sometimes desirable to increase the liquidvapor disengaging space in the inlet tubes. This prevents priming-the blowing of liquid slugs through the tubes causing pressure surges. Another advantage of increased liquid-Vapor disengaging space is the percentage increase of vaporization near the inlet, thus releasing a larger portion of the remaining fin-tube heat transfer area for superheating the gas. This results in larger overall heat transfer than would be obtainable in a similar sized vaporizer without the increased liquidvapor disengaging space.

Fig. 3 illustrates such a modified tube arrangement that is applicable for any pressure but preferred for operation below the critical pressure of the liquefied gas. Elements have been assigned reference numbers by adding 100 to the equivalent elements of Figs. 1 and 2.

The embodiment of the invention shown in Fig. 3 consists of a plurality of tins 102, a serpentine tube coil 103 positioned on and bonded to each of the fins, inlet manifold means 105 at the bottom of the vaporizer, and enlarged liquid boiling tubes 112. In Fig. 3, two inlet tubes 112 are shown to more fully utilize the available n heat transfer area. It is to be understood that any desired number of inlet tubes may be used. The inlet manifold 105 supplies the volatile liquid to the tubes 112 which in turn are connected by branch connections 122 to the lower end of tubes 103. The vaporized liquid is collected by the outlet manifold at the top of the vaporizer in a manner similar to that employed in the embodiment shown in Figs. 1 and 2.

The embodiment of the invention shown in Figs. 1 and 2 may be operated either horizontally or vertically as the physical arrangement demands. The Fig. 3 ernbodiment must be placed vertically, as shown. A horizontal orientation would not utilize the large inlet liquid-vapor disengaging space, and priming would cause poor heat transfer.

Although the vaporizer shown in Figs. 1 and 2 is of the counter-current type, it is to be understood that the invention is equally applicable to a co-current relationship between the flow of volatile liquid and atmospheric air. The circulating air is cooled almost linearly and very slowly so that the direction of air iow is determined by the most practical mechanical arrangement.

The vaporizer of the present invention may be operated with or without forced air circulation, depending on the capacity and rate at which the volatile liquid is to be vaporized. If the required capacity is sufficiently low, natural air circulation may be used with no external power source. On the other hand, with a high capacity requirement, an external power source is required to drive the fan or other means of obtaining forced air circulation.

It has been found that atmospheric vapon'zers in accordance with the present invention can successfully opcrate out-of-doors under the severest weather conditions. For example, an atmospheric vaporizer of the type herein disclosed, having a capacity of 3,000 cu. ft. per hr. at normal temperature and pressure, was built and successfully operated for a continuous Ll3hour period with an ambient air temperature between 25 F. and 40 F. and the relatively humidity above 68%. Although ice and frost deposited on the coils and fins under these conditions, the heat transfer was sufficient to vaporize the required quantity of liquid oxygen, and the ice formation did not build up sufficiently to block the atmospheric` air passages between the fins. It is pointed out that if the volatile liquid flow to the atmospheric vaporizer is reduced sufiiciently the unit could be continuously operated for an indefinite period.

What is claimed is:

l. In an atmospheric vaporizer having a plurality of spaced parallel fins of heat conducting material and a heat conducting fluid conduit having a plurality of serpentine bends positioned in heat exchange contact with each of said plurality of fins over substantially all of the length of said ns, the method of operation which comprises concurrently passing a quantity of volatile liquid into the same ends of each of said uid conduits; passing atmospheric air between and in heat exchange contact with said plurality of spaced parallel fins; collecting vaporized volatile liquid from the opposite ends of said heat conducting fluid conduits; and maintaining each of the variable heat transfer parameters at a value to provide a total heat transfer in accordance with the equation:

AB(TA-Tv)t1/2 Tanh kt B 2kg l;

N :number of vaporizer fins 2. An atmospheric vaporizer for vaporizing liquefied gas comprising a plurality of spaced parallel fins of heat conducting material; a heat conducting parallel-flow fluid conduit having a plurality of serpentine bends, positioned in the air space between an adjacent pair of said plurality of spaced fins, and secured on one side in heat exchange contact with one of said fins over substantially all the length of the fins to increase the contact area between said fluid conduits and said fins; inlet manifold means communicating with one end of each of said duid conduits for introducing a volatile liquid into the same end of each of said uid conduits; outlet manifold means communicating with the other end of said fluid conduits for collecting vapors of said volatile liquid from said plurality of fluid conduits; means for passing atmospheric air unidirectionally in parallel-flow streams between and in heat exchange contact with said plurality of spaced parallel fins; and a plurality of parallel-flow :conduit means, one associated with each of said fins, positioned in heat exchange :contact therewith and communicating between said inlet manifold means and one of said uid conduits, said plurality of parallel-110W `conduit means 6 of substantially greater total cross-sectional area than that of each of said fluid conduits.

References Cited in the file of this patent UNITED STATES PATENTS 1,961,070 Murphy May 29, 1934 2,138,777 Zellhoeffer Nov. 29, 1938 2,229,940 Spofford Jan. 28, 1941 2,560,453 Kleist July 19, 1951 2,729,074 Monroe et al. Ian. 3,1956 

